diff --git a/doc/BUILDING-external-libs-64-bit.md b/doc/BUILDING-external-libs-64-bit.md
new file mode 100644
index 00000000..173b58d3
--- /dev/null
+++ b/doc/BUILDING-external-libs-64-bit.md
@@ -0,0 +1,215 @@
+# BUILDING external libs (64-bit)
+
+## Prepare Ubuntu environment
+
+```
+sudo apt-get install build-essential cmake tofrodos libtool-bin
+sudo mkdir /opt/android
+sudo chown $LOGNAME /opt/android
+```
+
+## Install Android NDK
+```
+cd /opt/android
+wget https://dl.google.com/android/repository/android-ndk-r15c-linux-x86_64.zip
+unzip android-ndk-r15c-linux-x86_64.zip
+android-ndk-r15c/build/tools/make_standalone_toolchain.py --api 21 --stl=libc++ --arch aarch64 --install-dir /opt/android/tool64
+```
+
+## Build OpenSSL
+Best is to compile openssl from sources. Copying from your phone or elsewhere (don't!) ends up in misery.
+
+### Setup environment
+```
+cd /opt/android
+wget https://wiki.openssl.org/images/7/70/Setenv-android.sh
+fromdos Setenv-android.sh
+```
+
+Apply the following patch:
+```
+--- a/Setenv-android.sh
++++ b/Setenv-android.sh
+@@ -22,12 +22,12 @@
+ # list in $ANDROID_NDK_ROOT/toolchains. This value is always used.
+ # _ANDROID_EABI="x86-4.6"
+ # _ANDROID_EABI="arm-linux-androideabi-4.6"
+-_ANDROID_EABI="arm-linux-androideabi-4.8"
++_ANDROID_EABI="aarch64-linux-android-4.9"
+ 
+ # Set _ANDROID_ARCH to the architecture you are building for.
+ # This value is always used.
+ # _ANDROID_ARCH=arch-x86
+-_ANDROID_ARCH=arch-arm
++_ANDROID_ARCH=arch-arm64
+ 
+ # Set _ANDROID_API to the API you want to use. You should set it
+ # to one of: android-14, android-9, android-8, android-14, android-5
+@@ -36,7 +36,7 @@
+ # Android 5.0, there will likely be another platform added (android-22?).
+ # This value is always used.
+ # _ANDROID_API="android-14"
+-_ANDROID_API="android-18"
++_ANDROID_API="android-21"
+ # _ANDROID_API="android-19"
+ 
+ #####################################################################
+@@ -121,6 +121,9 @@
+ 	arch-arm)	  
+       ANDROID_TOOLS="arm-linux-androideabi-gcc arm-linux-androideabi-ranlib arm-linux-androideabi-ld"
+ 	  ;;
++	arch-arm64)	  
++      ANDROID_TOOLS="aarch64-linux-android-gcc aarch64-linux-android-ranlib aarch64-linux-android-ld"
++	  ;;
+ 	arch-x86)	  
+       ANDROID_TOOLS="i686-linux-android-gcc i686-linux-android-ranlib i686-linux-android-ld"
+ 	  ;;	  
+@@ -198,6 +201,14 @@
+ export ARCH=arm
+ export CROSS_COMPILE="arm-linux-androideabi-"
+ 
++if [ "$_ANDROID_ARCH" == "arch-arm64" ]; then
++	export MACHINE=aarch64
++	export RELEASE=2.6.37
++	export SYSTEM=android
++	export ARCH=aarch64
++	export CROSS_COMPILE="aarch64-linux-android-"
++fi
++
+ if [ "$_ANDROID_ARCH" == "arch-x86" ]; then
+ 	export MACHINE=i686
+ 	export RELEASE=2.6.37
+```
+Then:
+```
+export ANDROID_NDK_ROOT=/opt/android/android-ndk-r15c
+. ./Setenv-android.sh
+```
+and ignore error about FIPS_SIG.
+
+### Download and build OpenSSL
+```
+wget https://github.com/openssl/openssl/archive/OpenSSL_1_0_2l.tar.gz
+tar xfz OpenSSL_1_0_2l.tar.gz
+cd openssl-OpenSSL_1_0_2l/
+```
+Apply patch required to build for aarch64:
+```
+--- a/openssl-OpenSSL_1_0_2l/config
++++ b/openssl-OpenSSL_1_0_2l/config
+@@ -871,6 +871,7 @@
+   *-*-qnx6) OUT="QNX6" ;;
+   x86-*-android|i?86-*-android) OUT="android-x86" ;;
+   armv[7-9]*-*-android) OUT="android-armv7" ;;
++  aarch64-*-android) OUT="android-aarch64" ;;
+   *) OUT=`echo $GUESSOS | awk -F- '{print $3}'`;;
+ esac
+ 
+--- a/openssl-OpenSSL_1_0_2l/Configure
++++ b/openssl-OpenSSL_1_0_2l/Configure
+@@ -474,6 +474,7 @@
+ "android","gcc:-mandroid -I\$(ANDROID_DEV)/include -B\$(ANDROID_DEV)/lib -O3 -fomit-frame-pointer -Wall::-D_REENTRANT::-ldl:BN_LLONG RC4_CHAR RC4_CHUNK DES_INT DES_UNROLL BF_PTR:${no_asm}:dlfcn:linux-shared:-fPIC::.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR)",
+ "android-x86","gcc:-mandroid -I\$(ANDROID_DEV)/include -B\$(ANDROID_DEV)/lib -O3 -fomit-frame-pointer -Wall::-D_REENTRANT::-ldl:BN_LLONG ${x86_gcc_des} ${x86_gcc_opts}:".eval{my $asm=${x86_elf_asm};$asm=~s/:elf/:android/;$asm}.":dlfcn:linux-shared:-fPIC::.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR)",
+ "android-armv7","gcc:-march=armv7-a -mandroid -I\$(ANDROID_DEV)/include -B\$(ANDROID_DEV)/lib -O3 -fomit-frame-pointer -Wall::-D_REENTRANT::-ldl:BN_LLONG RC4_CHAR RC4_CHUNK DES_INT DES_UNROLL BF_PTR:${armv4_asm}:dlfcn:linux-shared:-fPIC::.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR)",
++"android-aarch64","gcc:-march=armv8-a -mandroid -I\$(ANDROID_DEV)/include -B\$(ANDROID_DEV)/lib -O3 -fomit-frame-pointer -Wall::-D_REENTRANT::-ldl:SIXTY_FOUR_BIT_LONG RC4_CHAR RC4_CHUNK DES_INT DES_UNROLL BF_PTR:${aarch64_asm}:linux64:dlfcn:linux-shared:-fPIC::.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR)",
+ "android-mips","gcc:-mandroid -I\$(ANDROID_DEV)/include -B\$(ANDROID_DEV)/lib -O3 -Wall::-D_REENTRANT::-ldl:BN_LLONG RC4_CHAR RC4_CHUNK DES_INT DES_UNROLL BF_PTR:${mips32_asm}:o32:dlfcn:linux-shared:-fPIC::.so.\$(SHLIB_MAJOR).\$(SHLIB_MINOR)",
+ 
+ #### *BSD [do see comment about ${BSDthreads} above!]
+
+```
+```
+perl -pi -e 's/install: all install_docs install_sw/install: install_docs install_sw/g' Makefile.org
+./config shared no-ssl2 no-ssl3 no-comp no-hw no-engine --openssldir=/opt/android/openssl/android-21/
+make depend
+# Make sure we don't get versioned .so which Android can't deal with
+make CALC_VERSIONS="SHLIB_COMPAT=; SHLIB_SOVER=" MAKE="make -e" all
+mkdir -p /opt/android/openssl/android-21/lib
+echo "place-holder make target for avoiding symlinks" >> /opt/android/openssl/android-21/lib/link-shared
+make SHLIB_EXT=.so install_sw
+```
+
+### Make symlinks
+```
+cd /opt/android/tool64/sysroot/usr/include
+ln -s ../../../../openssl/android-21/include/openssl
+cd /opt/android/tool64/sysroot/usr/lib
+ln -s ../../../../openssl/android-21/lib/libssl.so
+ln -s ../../../../openssl/android-21/lib/libcrypto.so
+```
+
+## Build Boost
+```
+cd /opt/android
+wget https://sourceforge.net/projects/boost/files/boost/1.64.0/boost_1_64_0.tar.gz/download -O boost_1_64_0.tar.gz
+tar xfz boost_1_64_0.tar.gz
+(cd boost_1_64_0; ./bootstrap.sh)
+```
+The NDK r15c above gives errors about fsetpos and fgetpos not found(!?!), so we "just" comment them out in the include file:
+`nano /opt/android/tool32/include/c++/4.9.x/cstdio` (`//using ::fgetpos`, `//using ::fsetpos`)
+
+Then:
+```
+export PATH=/opt/android/tool64/aarch64-linux-android/bin:/opt/android/tool64/bin:$PATH
+./b2 --build-type=minimal link=static runtime-link=static --with-chrono --with-date_time --with-filesystem --with-program_options --with-regex --with-serialization --with-system --with-thread --build-dir=android64 --stagedir=android64 toolset=clang threading=multi threadapi=pthread target-os=android stage
+```
+
+## Build & prepare zeromq
+Only needed for zeromq versions (>v0.11.0.0).
+```
+cd /opt/android
+git clone https://github.com/zeromq/zeromq3-x.git
+export PATH=/opt/android/tool64/aarch64-linux-android/bin:/opt/android/tool64/bin:$PATH
+export OUTPUT_DIR=/opt/android/zeromq
+./configure --enable-static --disable-shared --host=aarch64-linux-android --prefix=$OUTPUT_DIR LDFLAGS="-L$OUTPUT_DIR/lib" CPPFLAGS="-isystem /opt/android/tool64/include/c++/4.9.x -fPIC -I$OUTPUT_DIR/include -Wno-error -D__ANDROID_API__=21" LIBS="-lgcc"
+make
+make install
+
+git clone https://github.com/zeromq/cppzmq.git
+cp cppzmq/*.hpp zeromq/include/
+```
+
+## And finally: Build Monero
+```
+cd /opt/android
+git clone https://github.com/monero-project/monero
+cd monero
+```
+```
+# <patch monero code as needed>
+# also, don't abort on warnings (this is only an issue >v0.11.0.0):
+diff --git a/CMakeLists.txt b/CMakeLists.txt
+index 1f74f59..2c791c0 100644
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -400,7 +400,7 @@ else()
+     set(ARCH_FLAG "-march=${ARCH}")
+   endif()
+   set(WARNINGS "-Wall -Wextra -Wpointer-arith -Wundef -Wvla -Wwrite-strings -Wno-error=extra -Wno-error=deprecated-declarations -Wno-unused-parameter -Wno-unused-variable -Wno-error=unused-variable -Wno-error=undef -Wno-error=uninitialized")
+-  if(NOT MINGW)
++  if(NOT MINGW AND NOT ANDROID)
+     set(WARNINGS_AS_ERRORS_FLAG "-Werror")
+   endif()
+   if(CMAKE_C_COMPILER_ID STREQUAL "Clang")
+```
+```
+mkdir -p build/release.android64
+cd build/release.android64
+
+# only if not set already set
+export PATH=/opt/android/tool64/aarch64-linux-android/bin:/opt/android/tool64/bin:$PATH
+
+# for zeromq versions (>v0.11.0.0).
+CC=clang CXX=clang++ cmake -D BUILD_TESTS=OFF -D ARCH="armv8-a" -D STATIC=ON -D BUILD_64=ON -D CMAKE_BUILD_TYPE=release -D ANDROID=true -D BUILD_TAG="android" -D BOOST_ROOT=/opt/android/boost_1_64_0 -D BOOST_LIBRARYDIR=/opt/android/boost_1_64_0/android64/lib  -D OPENSSL_ROOT_DIR=/opt/android/openssl/android-21 -D CMAKE_POSITION_INDEPENDENT_CODE:BOOL=true -D ZMQ_INCLUDE_PATH=/opt/android/zeromq/include -D ZMQ_LIB=/opt/android/zeromq/lib/libzmq.a ../..
+
+# for pre-zeromq versions (<=v0.11.0.0).
+CC=clang CXX=clang++ cmake -D BUILD_TESTS=OFF -D ARCH="armv8-a" -D STATIC=ON -D BUILD_64=ON -D CMAKE_BUILD_TYPE=release -D ANDROID=true -D BUILD_TAG="android" -D BOOST_ROOT=/opt/android/boost_1_64_0 -D BOOST_LIBRARYDIR=/opt/android/boost_1_64_0/android64/lib  -D OPENSSL_ROOT_DIR=/opt/android/openssl/android-21 -D CMAKE_POSITION_INDEPENDENT_CODE:BOOL=true ../..
+
+make
+
+find . -name '*.a' -exec cp '{}' lib \;
+```
+Ignore the warning from the last command - all static libraries are now in `lib`.
+
+# Bringing it all together
+- Copy all .a libraries into the appropriate `external-libs` folders.
+- Copy `/opt/android/monero/src/wallet/wallet2_api.h` into `external-libs/monero/include`
\ No newline at end of file